The rapid increase in carbon dioxide emissions from industrial sources has been considered as one of the main causes of climate change. Carbon dioxide is one of the greenhouse gases and its atmospheric concentration has increased at an annual rate of about 2 ppm, and thus, the development of efficient carbon dioxide capture technologies is essential for the future of carbon-based energy. The reduction of carbon dioxide emissions can be achieved by improving energy efficiency, implementing renewable carbon-free energy sources, and developing carbon capture, utilization and storage (CCUS) technologies.
Worldwide energy use will continue increasing; thus, CCUS could provide an immediate solution to the global carbon imbalance. If CCUS technologies can incorporate renewable energy, their overall sustainability will be further improved. Most of the focus in the CCUS field has been placed on using amine-based solvents that react with gaseous carbon dioxide to form carbamates, thus capturing the carbon dioxide. Among the amine-based solvents, monoethanolamine (MEA) is one of the most favored solvents for carbon dioxide capture due to its high carbon dioxide capture capacity and fast reaction kinetics. In many CCUS schemes, the MEA process is combined with geological storage of the captured carbon dioxide. While these technologies have already been demonstrated in large scales, the MEA process and geological storage of carbon dioxide still face challenges such as high parasitic energy consumption during solvent regeneration and the permanence and accountability issues for long-term carbon dioxide storage. In addition, MEA has high volatility, and therefore, its corrosive fume is a concern for the process design and operation. The concentration of MEA has to be limited to 15-30 wt % and this makes the carbon dioxide capture and the solvent regeneration processes complicated and costly.
In answer to these concerns associated with MEA, a number of innovative organic and inorganic materials including amine functionalized solid mesoporous sorbents and liquid solvents, i.e., ionic liquids and organic solvents such as aminosilicone, are being developed to capture carbon dioxide. Ionic liquids are particularly intriguing since they generally exhibit negligible vapor pressure even at elevated temperatures. Ionic liquids can be synthesized with task-specific functional groups, (e.g., amine groups for carbon dioxide capture, and they can also possess interesting features such as reversible and phase changing behaviors. The current drawbacks of ionic liquids as carbon dioxide capture media include their complex synthesis and purification steps, and high cost.